Bottom Line:
Inhibition of CAR-1 by RNA-mediated depletion or mutation results in a specific defect in embryonic cytokinesis.This cytokinesis failure likely results from an anaphase spindle defect in which interzonal microtubule bundles that recruit Aurora B kinase and the kinesin, ZEN-4, fail to form between the separating chromosomes.Cumulatively, our results suggest that CAR-1 functions with CGH-1 to regulate a specific set of maternally loaded RNAs that is required for anaphase spindle structure and cytokinesis.

ABSTRACTCytokinesis completes cell division and partitions the contents of one cell to the two daughter cells. Here we characterize CAR-1, a predicted RNA binding protein that is implicated in cytokinesis. CAR-1 localizes to germline-specific RNA-containing particles and copurifies with the essential RNA helicase, CGH-1, in an RNA-dependent fashion. The atypical Sm domain of CAR-1, which directly binds RNA, is dispensable for CAR-1 localization, but is critical for its function. Inhibition of CAR-1 by RNA-mediated depletion or mutation results in a specific defect in embryonic cytokinesis. This cytokinesis failure likely results from an anaphase spindle defect in which interzonal microtubule bundles that recruit Aurora B kinase and the kinesin, ZEN-4, fail to form between the separating chromosomes. Depletion of CGH-1 results in sterility, but partially depleted worms produce embryos that exhibit the CAR-1-depletion phenotype. Cumulatively, our results suggest that CAR-1 functions with CGH-1 to regulate a specific set of maternally loaded RNAs that is required for anaphase spindle structure and cytokinesis.

Mentions:
RNAi-based functional genomic screens of C. elegans, in which embryos that were laid by RNA-treated worms were imaged by DIC microscopy, identified several genes that are required for cytokinesis (Gönczy et al., 2000; Piano et al., 2000; Zipperlen et al., 2001; Sönnichsen et al., 2005). One of these, Y18D10a.17, was a previously uncharacterized, but widely conserved, 340-aa protein containing a predicted RGG box and an atypical Sm domain, two motifs that are found commonly in RNA-binding proteins (Fig. 1 A). Consistent with the sequence predictions, purified GST fusions with the Sm domain and the RGG box bound to immobilized RNA (poly(U)-sepharose) beads (Fig. S1; available at http://www.jcb.org/cgi/content/full/jcb.200506124/DC1). Based on the primary sequence features and depletion phenotype, we and other investigators have named this gene car-1, for cytokinesis/apoptosis/RNA.

Mentions:
RNAi-based functional genomic screens of C. elegans, in which embryos that were laid by RNA-treated worms were imaged by DIC microscopy, identified several genes that are required for cytokinesis (Gönczy et al., 2000; Piano et al., 2000; Zipperlen et al., 2001; Sönnichsen et al., 2005). One of these, Y18D10a.17, was a previously uncharacterized, but widely conserved, 340-aa protein containing a predicted RGG box and an atypical Sm domain, two motifs that are found commonly in RNA-binding proteins (Fig. 1 A). Consistent with the sequence predictions, purified GST fusions with the Sm domain and the RGG box bound to immobilized RNA (poly(U)-sepharose) beads (Fig. S1; available at http://www.jcb.org/cgi/content/full/jcb.200506124/DC1). Based on the primary sequence features and depletion phenotype, we and other investigators have named this gene car-1, for cytokinesis/apoptosis/RNA.

Bottom Line:
Inhibition of CAR-1 by RNA-mediated depletion or mutation results in a specific defect in embryonic cytokinesis.This cytokinesis failure likely results from an anaphase spindle defect in which interzonal microtubule bundles that recruit Aurora B kinase and the kinesin, ZEN-4, fail to form between the separating chromosomes.Cumulatively, our results suggest that CAR-1 functions with CGH-1 to regulate a specific set of maternally loaded RNAs that is required for anaphase spindle structure and cytokinesis.

ABSTRACTCytokinesis completes cell division and partitions the contents of one cell to the two daughter cells. Here we characterize CAR-1, a predicted RNA binding protein that is implicated in cytokinesis. CAR-1 localizes to germline-specific RNA-containing particles and copurifies with the essential RNA helicase, CGH-1, in an RNA-dependent fashion. The atypical Sm domain of CAR-1, which directly binds RNA, is dispensable for CAR-1 localization, but is critical for its function. Inhibition of CAR-1 by RNA-mediated depletion or mutation results in a specific defect in embryonic cytokinesis. This cytokinesis failure likely results from an anaphase spindle defect in which interzonal microtubule bundles that recruit Aurora B kinase and the kinesin, ZEN-4, fail to form between the separating chromosomes. Depletion of CGH-1 results in sterility, but partially depleted worms produce embryos that exhibit the CAR-1-depletion phenotype. Cumulatively, our results suggest that CAR-1 functions with CGH-1 to regulate a specific set of maternally loaded RNAs that is required for anaphase spindle structure and cytokinesis.